I've a Goldberg Anniversary Cub that I bought about eight years ago at a swap meet. It was well built and has gotten a lot of flight time over the years.

Last week it went off the runway into the tall grass and when retrieving I noted the cowling mounting screws had shifted and after inspecting, the engine itself was slightly loose. When home and digging into what was going on, the answer came quickly that the firewall was fuel soaked and crumbling. A test of the tank under water confirmed what was suspected, the tank was leaking around the stopper and each time it got hung by its tail wheel, the firewall got another dose of fuel.

Fortunately the fuel soaking was mostly to the firewall itself as the builder had epoxy washed the fuel compartment and what seemed to happen is that the fuel followed the two fuel tubes that were fitted into snug hoes through the firewall where the fuel had opportunity to soak into the grain structure of the firewall plywood and spread. The entire firewall was soaked and crumbling but thankfully the fuel soaking was blocked by the glue joints around the firewall perimeter from invading the longerons.

The forward deck needed removed to get access to remove and replace the firewall and the effort was reasonably straightforward with a new deck and because the windscreen had been repaired with cellophane tape, a new windscreen.

The cause was the aging stopper. It can be noted that the stopper was well tensioned when installed as indicated by its thickness in comparison to a new but time takes its toll and the elastic qualities of the stopper had long since been lost.

So, if hanging a plane by its tailwheel, be warned to do maintenance on the tank if the plane is gaining age.